The Federal Aviation Administration (FAA) operates our national airspace (NAS). Airspace users of the NAS include air carriers (airlines), general aviation users, and military users. The FAA provides Air Traffic Management (ATM) services, including Air Traffic Control (ATC) services, to separate aircraft, and Traffic Flow Management (TFM) services to manage congestion associated with a resource. As used herein, “resource” refers to a sector or group of sectors in one or more Air Route Traffic Control Centers (ARTCCs) and to a region of airspace surrounding an airport, where congestion is managed by imposition of air traffic flow restrictions (“flow restrictions”) on inbound traffic upstream of the resource. With reference to a given flight, the airport may be a destination airport or an origin airport.
When congestion problems exist or are anticipated to exist (i.e., when the traffic demand exceeds the resource capacity), the FAA invokes TFM flow restrictions to control flows through a combination of departure delays, ground stops, route changes (reroutes), altitude changes (capping), and the spacing/metering of en route traffic and/or arrivals. Congestion problems may occur when traffic demand exceeds airspace/airport capacity (e.g., rush hour or situations where traffic is deviated from elsewhere), and/or when actual capacity is lowered from nominal levels due to weather and/or the loss of NAS capabilities (e.g., loss of communications, navigation, or surveillance services).
TFM flow restrictions are managed on a continuum from the strategic to the tactical. Strategic TFM is coordinated by the FAA's ATC System Command Center (ATCCC) in Herndon Va. Strategic flow restrictions for a given resource typically involve large amounts of traffic, multiple ATC facilities, and time horizons or lead times on the order of 1.5–6 hours or more before the actual congestion or other problem is predicted to occur. Strategic flow restrictions are coordinated through the ATCSCC and implemented by the local ATC facilities that control the actual traffic. The national Ground Delay Program (GDP) is an example of a strategic flow restriction. Tactical TFM typically involves smaller amounts of traffic, one or a few local ATC facilities in close proximity, and time horizons on the order of a few minutes to 2 hours. Arrival metering via the Center TRACON Automation System (CTAS) Traffic Management Advisor (TMA) or Multi-center TMA (McTMA) is an example of a tactical flow restriction.
Previous CTAS studies include studies on the integration of user and ATM systems (e.g., integrating the airborne Flight Management System (FMS) with CTAS) to enable user-preferred four-dimensional (4D) trajectories. The initial focus had been on optimization of trajectories in the presences of flow constraints such as required times of arrival (RTA) for arrival metering. However, it has become apparent that it is equally important, if not more so, to negotiate the selection of RTA for each flight, as contrasted with the trajectory selected to meet the RTA. RTA negotiation was proposed by S. M. Green, W. den Braven, and D. H. Williams in “Development and Evaluation of a Profile Negotiation Process for Integrating Aircraft and Air Traffic Control Automation,” NASA Technical Memorandum 4360, April 1993.
Interactions with the ATC coordinator of United Airlines during the 1993/94 CTAS TMA field tests at Denver Center confirmed the desire for users to collaborate on arrival metering, not just to determine an RTA, but also for arrival sequences. Sequences are less challenging to negotiate than specific RTAs, and provide a mechanism for an airline to influence the order of an arrival bank and move a later-arriving aircraft to an earlier position in a queue while moving earlier flights to later positions. This concept was further defined by S. M. Green, T. Goka, and D. H. Williams in “Enabling User Preferences Through Data Exchange,” AIAA 97-3682, AIAA Guidance, Navigation and Control Conference, New Orleans, La., Aug. 11–13, 1997. The concept evolved into a Distributed Air-Ground Traffic Management (DAGTM) approach for User-Preferred Arrival Metering, as discussed by S. M. Green, K. Bilimoria., and M. G. Ballin in “Distributed Air-Ground Traffic Management for En route Flight Operations,” AIAA 2000-4064, Guidance, Navigation, and Control Conference, Denver Colo., August 2000.
One problem encountered is that airspace users want to influence the priority of the users' flights that are subject to TFM flow restrictions. In many cases, a single flight may be impacted by more than one flow restriction as the aircraft moves across the NAS from one ATC facility or resource to another. Once an aircraft is airborne, many factors may influence its actual arrival time, including deviations for flow restrictions. Airspace user preferences include flight sequence and schedule (arrival time), among others. If flights are to be delayed and/or deviated, the users may value certain flights more over others (e.g., to maintain the integrity of the user's overall network schedule). Airspace users want to minimize delays for more than one flight, by optimizing the use of the user's fleet and by maintaining the integrity of the user's network schedule and airport arrival and departure banks.
The FAA and airspace users have achieved much progress over the past decade in the application of Collaborative Decision Making (CDM) principles to flow restrictions. CDM involves the sharing of data between the FAA and users to develop a common situation awareness and collaborative methods for making decisions that affect traffic flows and individual flights. Limitations are present, particularly with respect to a lack of CDM processes for tactical flow restrictions on a local and regional level.
Some of the objectives are to facilitate CDM for flow restrictions on a local and regional level, to allow users to identify queue sequence preferences and priorities for the users' flights as an aircraft enters and/or moves across sectors with flow restrictions throughout the NAS, to credit an aircraft for flow restriction impacts the aircraft absorbs relative to other aircraft, and to enable the FAA, through the TFM system, to equitably accommodate those priorities.
Airspace users are primarily interested in arriving on time and maintaining the user's network schedule, second only to the safe operation of the user's flights. Special problem characteristics arise from the individual nature of flow restrictions and how these restrictions affect individual flights within the NAS.
(1) Flow restrictions vary in form. Two types of flow restrictions are relevant here: Metering/Spacing; and changes to the route or planned altitude profile. Relatively few Metering/Spacing restrictions (such as TMA arrival metering) are time-based today, but this circumstance will change as TMA is deployed to serve more airports, and as Regional Metering enhancements are implemented within a Multi-Center TMA (McTMA) to enable time-based en route metering. Nevertheless, Metering/Spacing restrictions restrict the rate of flow of a stream of flights through a fix or airspace (e.g., 60 flights/hour or 10 miles in trail). Flight trajectories are typically modified by air traffic controllers to conform to such restrictions (i.e., adjustments in speed, heading, and/or altitude to delay the flight), but the trajectories are not necessarily changed to avoid a region of airspace. Alternatively, the second type of restriction involves a change to the route and/or altitude profile of a flight to physically move the flight to another region of airspace. For example, a flight might be rerouted to another arrival fix to enter a congested terminal area from a less congested direction, or a flight might be rerouted (or restricted in altitude) to completely avoid a congested sector/region of airspace. In summary, the first type of restriction focuses on managing the flow-rate while the second type focuses on moving a flight to another region of airspace. Both types of restrictions may be applied to aircraft in various phases of flight from pre-departure (pushback and take-off), departure/ascent, en route, and arrival/descent. Any one flow restriction may involve multiple flights in various phases of flight (e.g., spacing for en route congestion may involve some flights from nearby airports that have not yet departed as well as airborne flights that are airborne and will be transiting the impacted sectors in cruise or ascent/descent to/from cruise altitude. Both types of restrictions will affect delay, either directly in the case of metering/spacing, or indirectly in the case of reroute/altitude flow restrictions.
(2) If an aircraft is delayed by one flow restriction earlier in its flight (e.g., delay in departure or in push-back from a gate), the aircraft loses its original place relative to other flights as the aircraft progresses downstream. As a result, sequentially-experienced flow restrictions accumulate. If congestion-based queues form downstream, the previously restricted aircraft enters the queue later and loses its position and priority, relative to other aircraft. that would have nominally been scheduled to arrive near the same time.
(3) The operational impact of CDM for flight priority/sequence grows with the time horizon over which such priority is in effect. Users need to be able to compete or negotiate for flight priority over time horizons that are significantly greater than what is available for individual tactical flow restrictions.
(4) To effectively leverage user-preferred sequences and priorities, a user needs to be able to “collaborate” with TFM over most, if not all, of the user's flights that contribute to a flow restriction. If a user is restricted to priorities within the user's own fleet, there may be little benefit in asserting a flight priority.
(5) Equitable access to airspace and ATM services is a fundamental desire of airspace users.
(6) It is not equitable to enable one user's preferred sequence/flight priority at the cost of negatively impacting another user's delay. Sequences preferred between flights of a first user may be fair as long as these preferences don't add unacceptable net delays and/or penalties to a second user's flights.
(7) When en route and arrival metering restrictions are enforced, an ARTCC often restricts internal departures on a tactical basis, pending designation of an APREQ departure-release time by the ARTCC, in order to insert the aircraft departure into an unoccupied time slot in the restricted overhead traffic stream. If the overhead stream is already full at the time of the departure request, the aircraft is often held on the ground until a time slot occurs upstream, resulting in an inequitable delay for departure of the aircraft relative to the overhead traffic.
What is needed is an approach that (1) allocates and accumulates aircraft flight delay credits to each of a collection of one or more aircraft that experiences one or more flow restrictions relative to one or more resources (sector or airport), (2) allows bidding of part or all of the accumulated delay credits for priority handling of an individual aircraft in response to imposition of a flow restriction on a flight or group of flights, and (3) facilitates transfer or trading of delay credits among two or more aircraft flights, for the same airline or for different airlines, in a queue or in different queues. Preferably, the approach should integrate allocation, accumulation and consumption of flow restriction-based delay credits and should ensure that such delay credits are not monopolized by one or a few airlines.